1. Field of Invention
The present invention relates to automatic injectors, and more particularly, to automatic injectors that reduce the likelihood of coring a sealing member.
2. Discussion of Related Art
Automatic injectors are well known. Basically an automatic injector is a device for enabling an individual to self-administer, or administer to another, a dosage of a liquid medicament. An advantage of automatic injectors is that they contain a measured dosage of a liquid medicament in a sealed sterile condition capable of storage in such condition for an extensive period of non-use, during which period immediate injection of the stored dosage may be accomplished at any time under severe emergency conditions. Another advantage of automatic injectors is the administration of the self-contained dosage of liquid medicament is accomplished without the necessity of the user initially seeing the hypodermic needle through which the liquid medicament is injected or of manually penetrating such visible needle into the user's or another person's tissue.
As stated above, automatic injectors are particularly suited for use under emergency conditions. For example many tens of millions of such automatic injectors have been manufactured and sold containing nerve gas antidotes for use under emergency chemical warfare conditions. Typical units which have been utilized for this purpose are disclosed in U.S. Pat. Nos. 2,832,339, 3,882,863, and 4,031,893. In addition units of this type have been manufactured and used in administering anti-arrhythmic medicaments under emergency conditions relating to hart attack medical situations. The use of an auto injector has also been proposed to provide other medicaments useful in treating heart attack symptoms such as clot selective thrombolic agents (for example, tPA) and related medicaments. See for example, U.S. Pat. Nos. 4,689,042, 4,755,169, and 4,795,433. In addition, automatic injectors have been widely marketed containing a dosage of epinephrine as an antidote for counteracting severe allergic reactions, as for example, to bee stings, and the like.
In all of these instances, the auto-injector is specifically structured so that in its normal operation the needle extends into the tissue of the individual and a specified amount of liquid medicament stored in a cartridge within the injector is injected into the tissue of the individual.
The hypodermic needle of an autoinjector has a forward end adapted to penetrate the clothing and flesh of an individual and a rearward end adapted to communicate with a liquid medicament source so that the medicament is permitted to flow from the source, through the central longitudinal bore or lumen in the needle, and into the flesh of the individual. In some embodiments, the needle is contained inside the cartridge containing the liquid medicament. For example one application exists in the field of automatic injection devices, wherein the liquid medicament is sealed within a tubular container or cartridge, generally made of glass, plastic or metal, having a rubber seal closing off at the forward end and a rubber plunger at the rearward end. For example see U.S. Pat. No. 5,354,286. During an injection operation, a stressed spring assembly is released moving a push rod against the plunger. The plunger pushes against the hub-end of the needle causing the needle to puncture the forward end seal of the cartridge and penetrates into the flesh of an individual. The liquid medicament is pushed at the same time through the needle, thus releasing the medicament into the individual's flesh.
In another type of automatic injector, the needle is connected to the forward end of the cartridge. See U.S. Pat. No. 5,102,393. During an injection operation, the needle is forced through a resilient seal at the forward end of the outer housing or through an elongated rubber sheath surrounding the needle. In either case the needle is kept sterile by a seal disposed toward a forward end of the housing while the injector is stored. After the needle punctures the seal or sheath, it then is forced into the flesh of the individual.
An issue that must be dealt with in each of the mentioned arrangements is that the forward end of the needle must perforate a rubber or other type of seal, and it is possible for the forward end of the needle to core out or dislodge a small particle of material from the seal and potentially block the needle orifice/lumen or be forced into the individual's flesh.